Absorption process for gas separation

ABSTRACT

In a process of separating a readily adsorbable gas and a less readily adsorbable gas separately from a mixture of these gases by introducing the gas mixture into an adsorption column containing an adsorbent to adsorb thereon the readily adsorbable gas and then recovering the adsorbed gas by desorbing it under a reduced pressure, the purity of the readily adsorbable gas thus recovered is greatly increased by purging the adsorption column prior to the desorption step with a pure gas having almost the same composition as the adsorbed gas at an almost same pressure as that in the adsorption step. Also, by introducing into the column a pure gas having the same composition as the less readily adsorbable gas prior to the introduction of the gas mixture, the less readily absorable gas is recovered in a high pure state in the above gas recovery process.

United States Patent [191 Tamura 1 1 Mar. 19, 1974 ABSORPTION PROCESSFOR GAS Primary ExaminerCharles N. Hart SEPARATION Attorney, Agent. orFirm-Wenderoth, Lind & Ponack [76] inventor: Takaai Tamura, No. 5-7,2-chome Kitano, Mitaka-shi, Tokyo, Japan S R CT [22] Filed: Mar. 17,1972 In a process of separating a readily adsorbable gas and Appl. No.:235,487

a less readily adsorbable gas separately from a mixture of these gasesby introducing the gas mixture into an adsorption column containing anadsorbent to adsorb thereon the readily adsorbable gas and thenrecovering the adsorbed gas by desorbing it under a reduced pressure,the purity of the readily adsorbable gas thus recovered is greatlyincreased by purging the adsorption column prior to the desorption stepwith a pure gas having almost the same composition as the ad sorbed gasat an almost same pressure as that in the adsorption step. Also, byintroducing into the column a pure gas having the same composition asthe less readily adsorbable gas prior to the introduction of the gasmixture, the less readily absorable gas is recovered in a high purestate in the above gas recovery process.

6 Claims, 3 Drawing Figures PATENIEBIIAR 19 m'r-t SHEEI 2 [If 3 Fig. 2

PAIENIEDIAR 19 I974 SHEET 3 (IF 3 1 ABSORPTION PROCESS FOR GASSEPARATION DISCLOSURE OF THE INVENTION The present invention relates toseparating gases from a gas mixture by an adsorbent and moreparticularly, the invention relates to a process for separating in anindustrial scale from a gas mixture the gas component which is mostreadily absorbed on an adsorbent (hereinafter, such a gas component iscalled readily adsorbable gas or gas component) in a high pure state.Still further, the invention relates to a process for recovering in anindustrial scale from a gas mixture the readily adsorbable gas componentand the component which is most weakly adsorbed on the adsorbent(hereinafter, such a gas component is called less readily adsorbable gascomponent") each in a high pure state.

Various attempts have been made for separating a specific gas componentor specific gas components by utilizing the selective adsorptiveproperty of each gas component in the gas mixture. In such conventionalgas separation processes, a gas mixture is introduced into an adsorptioncolumn packed with an adsorbent from one end thereof to adsorb thereadily adsorbable component. while recovering the less readilyadsorbable component as an enriched component from the opposite end ofthe column, and if necessary, the adsorbed component is also recoveredby heating or suction. Such a gas separation process by using adsorbenthas now been utilized in various fields and furthermore it has recentlybeen attempted to separate oxygen or nitrogen from air by using a kindof adsorbent called molecular sieve.

However, such known separation means are based on a simple combinationof an adsorption step and a desorption step and thus any of these knownprocesses have not yet been developed for obtaining high pure gases inan industrial or economical scale. In particular, it is accompanied withmany difficulties to recover high pure oxygen or nitrogen from air in anindustrial scale.

The inventor of the present invention has previously discovered animproved adsorption process for gas separation and has succeeded inrecovering a less readily adsorbable gas component from a gas mixturethereof in a high pure state and with a high efficiency (Japanese PatentApplication No. 73,l5l/l965). In particular, by practicing the improvedadsorption process using the specific adsorbent prepared by treating anaturally occurring tuff as will be described below in detail, it hasbeen possible to separate high pure oxygen from air.

According to my improved process, in the case of conducting theadsorption process by subjecting first the adsorption column to adesorption procedure under a reduced pressure (desorption step) and thenintroducing a gas mixture into the adsorption column from an end thereofand while maintaining the pressure in the column at normal pressure or adefinite pressure higher than the normal pressure, continuing theintroduction of the gas mixture, whereby the readily adsorbable gascomposition is adsorbed on the adsorbent and at the same time the lessreadily adsorbable component is recovered from the opposite side of thecolumn in a pure state (adsorption step), by applying a feedback stepbetween the desorption step and the adsorption step, that is, byintroducing a high pure gas having the same composition as the lessreadily adsorbable gas into the column immediately after the completionof the desorption procedure until the pressure in the column reaches adefinite pressure, the break through curve can be sharpened and hencethe less readily adsorbable gas composition can be separated from thegas mixture in a high-pure state and with a high yield.

Moreover, when the improved adsorption process is conducted by employingthe specific adsorbent as will be explained below, high pure oxygencontaining less than 0.1 percent nitrogen can be separated from air.

However, the above process aims at the recovery of the less readilyadsorbable gas component and thus when the above process is applied forrecovering the readily adsorbable gas component, that is, recovering thegas component adsorbed on the adsorbent in a desorption step under areduced pressure, it is difficult to obtain the satisfactorily high pureproduct.

An object of the present invention is, accordingly, to provide a processof obtained in an industrial scale the readily adsorbable gas componentin a high pure state from a gas mixture by using an adsorbent.

Other object of this invention is to provide a process of separatingnitrogen in a high pure state from air in an industrial scale by usingthe specific adsorbent.

Further object of this invention is to provide a process of separatingboth of the readily adsorbable gas component and the less readilyadsorbable gas component separately from the gas mixture thereof each ina high pure state by using an adsorbent.

Still other object of the present invention is to provide a process ofrecovering in an industrial scale high pure oxygen and high purenitrogen separately from air by using the specific adsorbent.

As the results of various investigations, the inventor has discoveredthat by purging the adsorption column with a substantially pure gashaving the same composition as the readily adsorbable gas under the samepressure as that in the adsorption step after conducting the adsorptionstep and, if necessary, recovering the less readily adsorbable gas, andprior to recovering the readily adsorbable gas component adsorbed on theadsorbent by subjecting it to a desorption procedure at a reducedpressure, the readily adsorbable gas component can be recovered in anextremely high pure state in the subsequent desorption step.

In this case, the high pure purging gas is supplied from an outer sourceor tank in the first step, but the gas recovered in the desorption stepmay of course be used. Moreover, by combining the process of the presentinvention and the feedback step discovered previously by the sameinventor, the less readily absorbable gas component can be recovered ina high pure state together with the readily adsorbable gas component.Moreover, by using the specific adsorbent as mentioned below in theprocess of this invention, high pure nitrogen and high pure oxygen canbe separated from air.

Now, the invention will be explained by referring to the FIGURE in theaccompanying drawing, in which an embodiment of an adsorption column forconducting the process of this invention is illustrated.

in FIG. 1, an adsorption column 1 is packed with an adsorbent 2 such assilica gel, activated carbon, zeolite, etc., to provide an adsorptionunit. The adsorption column l is equipped with an inlet pipe 4 having avalve 3 and an outlet pipe 6 having a valve 6.

For the sake of simplicity, the example of this invention will beexplained about the case of separating nitrogen or nitrogen and oxygenfrom air by using the adsorbent, although the invention is not limitedto the case only. That is, as will be described in the examples of thisinvention, the process of this invention may be applied to the case of acarbon dioxide gas and oxygen each in a high pure state from a mixtureof these gases, the case of separating H and N, each in a high purestate from an ammonia decomposition gas, the case of separating valuablecomponents from various petroleum cracking gases, etc.

Now, in an embodiment of the present invention, the inlet 4 of theadsorption column 1 containing an adsorbent having a higher adsorptionpower to nitrogen than to oxygen is connected to a suction pump (notshown) and the valve 3 is opened, while the valve is closed. Thus, thecolumn is evacuated by means of the suction pump to remove thecomponents adsorbed on the adsorbent. Thereafter, air from whichmoisture and carbon dioxide have been previously removed (hereinaftersuch pre-treated air is called simply air in this specification) isintroduced into the adsorbent column through the inlet 4. When the innerpressure of the adsorption colum reaches normal pressure, the valve 5 isopened and the intrduction of air is further continued. Thus, nitrogenin the air is adsorbed on the adsorbent and a gas enriched with oxygenis withdrawn from the outlet 6 of the column. In this case, although thegas thus withdrawn is not so pure as being used for industrial purposes,the gas may be recovered if necessary. When the component of the gas atthe inlet 4 becomes almost the same as that of the gas at the outlet 6,the introduction of air is stopped. Thereafter, a pure nitrogen gasbegins to introduce from an outer nitrogen source into the column 1through the inlet 4. [n this case, the pressure in the column ismaintained at the pressure almost same as that in the introduction ofair. Also, because, the valve 5 at the outlet 6 of the column is in anopen state, when the introduction of air is continued, the excess gas isdischarged through the valve 5 from the outlet 6 of the adsorptioncolumn 1. By the operation, the oxygen remaining in the air in thecolumn and in the adsorbent is purged by the nitrogen gas. in this case,the purging gas may be introduced into the adsorption column from anyside of the column. For example, same results are obtained when the purenitrogen gas is introduced into the column from the conduit 6 anddischargedfrom the conduit 4.

When almost no oxygen is present in the gas at the outlet 6 in the caseof introducing the nitrogen gas from the inlet 4, the introduction ofthe nitrogen gas is stopped, the valve 5 is closed, and then the columnI is evacuated through the outlet 4, whereby the nitrogen in the columnand adsorbed in the adsorbent is recovered. This operation may beconducted by closing the valve 3 and evacuating from the pipe 6.

By the above-mentioned operation, high-pure nitrogen can be recoveredand also a desired amount ofsuch high pure nitrogen can be obtained byconducting the procedure repeatedly.

In other embodiment of the present invention, both of high-pure nitrogenand high-pure oxygen can be recovered from air. That is, afterconducting the desorption step of the adsorption column 1, pure oxygenis introduced in the column from an outer oxygen source and when theoxygen pressure introduced in the column reaches normal pressure, air isintroduced from the inlet 4 and at the same time high pure oxygen isrecovered from the outlet 6. in the step, nitrogen is adsorbed on theadsorbent. Just before nitrogen begins to be present at the gascomposition at the outlet end of the column, the introduction of air isstopped and then pure nitrogen is introduced into the column from theinlet 4 as mentioned above. Then, by conducting the same procedure asabove, pure nitrogen can be recovered. Thus, desired amounts of pureoxygen and pure nitrogen can be recovered from air by repeating theabove-mentioned process.

Furthermore, by employing the specific adsorbent as will be mentionedbelow as the third embodiment of this invention, very high-pure nitrogenor very highpure nitrogen and very high-pure oxygen can be recoveredfrom air.

That is, in the third embodiment of this invention, the adsorbentprepared by pulverizing into proper grain sizes a naturally occuringtuff consisting mainly of SiO;, A1 0 and H 0, containing l-l0 weightpercent of alkali and alkaline earth metal oxides, and having the X-raydiffraction pattern shown in Table 1 or Table 2 and then subjecting itto a dehydration treatment by heating to about 350700C.

TABLE 1 latice latir distance intensity distance intensity A 10 I/l, Al0 Ill, l3.9:0.l 2 3.23 10.03 6 9.l:0.l 4 3.l0+0.03 0-l 6.6 t 0| 4 2.90z 0.03 3 6.5 i O.l 2 2.85 t 0.03 02 6110.] 2 2.7l 20.03 I 5.83 0.05 22.58 t 0.03 l 4.55 0.05 2 2.53 t 0.03 2 4.30 1 0. l0 0-5 2.49 I 0.03 0-44.26 i 0.10 0-2 2.47 1- 0.03 0-3 4.08 I 0.l0 0-4 2.45 i 0.03 0 2 4.05 1'0.10 0-6 2.04 t 0.03 2 4.0l 2: 0.05 7 L96 1 0.03 l 3.85 I 0.03 2 L88 10.02 l 3.8l IOJU 0-4 1.821002 l 3.77 1 0.05 l l.ll2 10.02 (l-2 3.48 i0.03 10 1.79 0.02 l 3.40 0.03 5 1.53 10.02 I 3.35 10.10 0-8 TABLE 2lalice latir distance distance intensity A l0 l/l,, A 10 1/1,, 9.l0t0.l7 3.|Bt0.03 4 7.99:0.l 4 3.15:0.03 4 6.82 t O.l 2 2.99 z 0.03 0l 5.85 i0.08 5 2.98 z 0.03 4 5.29 i 0.08 2 2.89 i 0.03 4 5. l2 1 0.05 3 2.850.03 O-2 4.67 i 0.05 2 2.81 0.03 3 4.30 I 0.10 0-5 2.74 0.03 l 4. 2 6 iw O-2 2.53 0.02 2 4.0811 0.10 0-4 2.49 i 0.03 0-4 4.05 i 0. l0 0-6 2.470.03 0-3 3.98 z 0.05 [0 2.46 0.02 2 3.85 i 0.05 2 2.45 0.03 0-2 3.81i0.l0 04 2.02 $0.02 0.5 3.77 i 0.05 2 L 0.02 0.05 3.47 z 0.03 7 L87 0.020.5 3.34:0.10 08 L81 0.02 0-2 3.35 1 0.03 5 1.72 0.02 0.5 3.22 i (103 4The material defined in Table l occurs mainly in the Tohoku and Chungokudistricts in Japan and the material defined in Table ll occurs in theTohoku and Kyushu districts.

Because the aforesaid adsorbent used in this invention in the specificembodiment can be prepared by a simple manner from a rock naturallyoccuring in a large amount, a large amount of the adsorbent is obtainedwith much lower cost than those of the adsorbents such as silica gel,alumina, activated carbon, etc. Moreover, the adsorption power of theadsorbent to nitrogen is generally higher than that of molecular sieve5A which is believed to show the highest adsorption power amongsynthetic zeolites under same temperature and pressure and inparticular, the adsorption power of the adsorbent prepared from the tuffhaving the X-ray diffraction pattern shown in Table I is 2.5 timeshigher than that of the molecular sieve 5A. Furthermore, it has beenconfirmed from the valve (specific adsorbance) showing how many times isthe concentration ratio of nitrogen to oxygen adsorbed on the adsorbenthigher than the concentration ratio of nitrgen to oxygen in the gas inequilibrium with the adsorbent that the value of synthetic zeolite isabout 2.5, while some of the adsorbent prepared from the naturallyoccuring tuff as mentioned above reaches 5. However, since the aforesaidexcellent property is greatly deteriorated by adsorbing carbon dioxidegas and moisture, it is necessary to use air containing no such harmfulcomponents.

Thus, because the adsorbent mentioned above has such excellent property,high-pure nitrogen and highpure oxygen can be recovered from air inlarge industrial scale by conducting the above-mentioned process of thisinvention as mentioned above using the adsorbent.

The above-mentioned dehydration treatment for the rock is conducted forremoving water attached to the rock and water of crystallization of therock and is conducted by heating generally the rock at about 350-700C.,preferably 400-600C. When the heating temperature is lower than 350C,the adsorbent prepared has poor adsorption power, while when thetemperature is higher than 700C, the structure of the rock is changed tosuch extent as being poor in practical use. As will be shown in Examples4, 5, and 6, by using these adsorbents high-pure nitrogen and oxygen ofabout 30-95 percent in purity could be recovered from air with goodefficiency.

The invention was explained above by referring to the example ofseparating nitrogen or nitrogen and oxygen from air but the sameexplanation can be applied to the separation of other gaseous mixturesby considering nitrogen and oxygen as a readily absorbable component anda less absorbable component in such gas mixture respectively.

The remakable merits of this invention will become apparent from thefollowing examples of this ll'lVElltlOP. That is, Reference 1 is acomparison case where carbon dioxide gas and oxygen were separated froma mixture of them using activated carbon according to a conventionalmanner, that is, without applying the purging procedure with a high-purecarbon dioxide gas prior to conducting the desorption procedure byevacuation. The purity of the carbon dioxide and oxygen gas obtained bythe conventional process were only 93.7 percent and 84.5 percent,respectively.

On the other hand. according to the process of Exampie 1 which is thefirst embodiment of the process of this invention, the purity of oxygenwas 84.5 percent but the purity of the carbon dioxide gas reached ashigh as 99.95 percent and further the amount of the carbon dioxide gasthus obtained was far larger than the amount used for the purgingprocedure. Furthermore. in Example 2 wherein the second embodiment ofthis invention was applied, the purity of oxygen was 95 percent andfurther the purity of the carbon dioxide gas was 99.95 percent, whichshowed that the two components were almost completely separated from thegas mixture.

The same was true in Reference 2 and Examples 3 and 4, wherein theadsorbents prepared by treating the naturally occuring tuffs were usedfor separating nitrogen or nitrogen and oxygen from air. Reference 2 wasconducted by a conventional process, while Example 3 was conducted bythe first embodiment of the process of this invention and Example 4 wasconducted by the second embodiment of this invention.

In Reference 2, the purity of the purest oxygen recovered was only 53percent (maximum concentration 65 percent). Also, when the recovery ofoxygen gas was continued until the composition of the gas at the outletbecame that of air, the purity of the oxygen-rich gas thus recovered wasonly M percent. Also, the purity of nitrogen in Reference 2 was only91.5 percent, while the purity of nitrogen recovered in Example 5 was99.94 percent. Furthermore, in Example 4 the purity of oxygen was alsoas high as 93 percent.

The invention will, now, be explained practically by referring to thefollowing examples.

REFERENCE l An adsorption colum having an inside diameter of 5 cm. andheight of cm. was packed with 940 g. of activated carbon of coconutshell. The column was preliminary evacuated by a suction pump and whenthe inside pressure of the column reached 20 mm. Hg, a l 1 mixture ofoxygen and carbon dioxide by volume ratio was introduced into the columnto raise the pres sure to normal pressure, and thereafter, the gasmixture was passed through the column at a speed of 4 liters/- min. atroom temperature and under normal pressure. When the concentration ofthe gas at the outlet became almost same as that at the inlet, theintroduction of the gas mixture was stopped. The volume of gas thusrecovered was 13.5 liters and the content of oxygen in the recovered gaswas 84.5 percent, the balance being carbon dioxide gas. Thereafter, thecolumn was evacuated and the gas was collected until the inside pressureof the column became 20 mm. Hg. The volume of the gas thus collected was11.5 liters under normal pressure and normal temperature and itcontained 93.7 percent carbon dioxide gas, the balance being oxygen.

EXAMPLE 1 Almost the same procedure was repeated as in Reference 1 byusing the same adsorption column and adsorbent except that thedesorption procedure was conducted after introducing 9.0 liters of acarbon dioxide gas of 99.9 percent in purity. The content of oxygen inthe gas at the outlet of the column at the end of the operation was lessthan 1 percent. The volume of the carbon dioxide gas recovered byevacuating the column until the inside pressure of the column reached 20mm. Hg. was 18.0 liters under normal temperature and normal pressure andthe purity of carbon dioxide was 99.95 percent.

EXAMPLE 2 The same procedure as in Example 1 was followed except thatprior to conducting the operation, oxygen of 95.0 percent in purity wasintroduced into the column until the pressure became normal pressurewithout introducing the gas mixture of oxygen and carbon dioxideimmediately after the initial desorption by evacuation. The volume ofthe oxygen gas was 18 liters and the purity was 95 percent. Also, thevolume of the carbon dioxide gas thus recovered was l8.0 liters and thepurity was 99.95 percent.

REFERENCE 2 A desorption column having an inside diameter of cm. and alength of I40 cm. was used. The adsorbent used was prepared from a tuffoccured in the Chugoku district in Japan. As the results of chemicalanalysis, the rock was confirmed to having the following composition:SK): 698% percenCKTKL 11.70 percent, Fe 1.76 percent, MgO trace, CaO1.72%, Na O 2.94%. K 0 1.79%, and H 0 10.76%.

Also, the X-ray diffraction pattern thereof was in the numeral rangesdescribed in Table l.

The tuff was pulverized into 10-20 mesh, heated for one hour to 550C.while passing dried air, and allowed to cool in a closed condition.Thereafter, 2.35 kg. of it was filled in the above column. Theadsorption column was connected to a vacuum pump and the column wasevacuated until the inside pressure of the column reached 50 mm. Hg.Then, air from which misture and carbon dioxide had been removed wasintroduced into the column to a normal pressure and thereafter, the airwas further passed through the column at a speed of 3 liters/min. Inthis case, the inside pressure of the column was maintained almost atthe atmospheric pressure. The maximum concentration of the oxygen in thegas discharged from the column was 65 percent and when the gasdischarged from the column was collected until the concentration of theoxygen became 35 percent, the volume thereof was 6.3 liters. The meanconcentration of oxygen in the recovered gas was 53 per cent. Also, whenthe introduction of the air was continued until the content of oxygen inthe gas at the outlet became 22 percent, the volume of the product gasthus recovered was 1 l .7 liters and and the mean oxygen concentrationwas 41 percent.

After the above procedure was over, the column was evacuated to 50 mm.Hg and the volume of the gas recovered was 2l.1 liters under normalpressure and the mean oxygen concentration of the gas was 8.5 percent.

EXAMPLE 3 The same procedure as in Reference 2 was followed except thatafter finishing the introduction of air in the column, nitrogen of 99.9percent in purity was introduced into the column from an end thereofwhile maintaining the inside pressure of the column at almost normalpressure and the gas inside the column was discharged from the oppositeend of the column. When 12 liters of the nitrogen gas was introducedinto the column, the content of oxygen in the gas discharged from thecolumn was about 1 percent. Thereafter, the column was evacuated bymeans of a suction pump until the pressure became 50 mm. Hg and thevolume of the gas recovered was 24.5 liters and the mean oxygenconcentration in the gas was only 0.06 percent.

EXAMPLE 4 The same procedure as Example 3 was followed except thatwithout introducing air into the column immediately after the end of thefirst evacuation for desorption, oxygen of 95 percent in purity wasfirst introduced until the inside pressure of the column became almostnormal pressure (10.7 liters of oxygen was required) and then air wasintroduced into the column while maintaining the inside pressure of thecolumn at almost normal pressure. When the oxygen-rich gas dischargedfrom the column was collected until the content of oxygen in the gas atthe outlet end of the column became percent, the volume of 14.7 litersof the gas was obtained and the mean oxygen concentration thereof was 93percent. Also, when the oxygen-rich gas was recovered until theconcentration of oxygen in the gas at the outlet end became 21.5percent, the volume of 19.8 liters of the gas was obtained and the meanoxygen concentration was 74 percent. Furthermore, the volume of a purenitrogen gas required for purging the column and the volume and purityof the nitrogen gas recovered at the evacuation step were almost same asthose in Example 3.

Now, the invention was described hereinbefore mainly in respect of thefundamental embodiments of this invention using only a single adsorptioncolumn and further the process of this invention can be practiced moreefficiently in industrial scale by employing a plurality of suchadsorption columns, which will be described below in detail.

That is, as mentioned above the feature of the present invention is inthe point of purging the adsorptoin column with a pure gas having thesame composition as that of the readily adsorbable component under thesame pressure as that in the adsorption processprior to the operation ofthe desorption procedure. The gas used for purging the adsorption columnmay be supplied from an outer source in the first purging step but forpracticing the process of this invention as economical and dependentseparation process, it is necessary to use the gas obtained in theprevious desorption step as the purging gas after then. That is, theamount of the readily adsorbable component capable of being separated inone desorption cycle is the amount of the desorbed gas minus the amountof the purging gas required for purging the adsorption column.Therefore, in order to separate the readily adsorbable componentefficiently and economically, it is necessary to reduce the amount ofthe purging gas as small as possible.

On the other hand, if the amount of the purging gas is reduced, the lessreadily adsorbable component apts to remain in the adsorption column tomake impure the desorbed gas in the desorption step. Thus, the desorbedgas recovered in the desorption step is unsuitable for the purging gasin the subsequent purging step and it becomes impossible to separate thereadily adsorbable gas component in a high pure state. In other words,if the embodiment as shown in FIG. 1 is practiced in an industrial scalefor obtaining the readily adsorbable gas component in a high pure state,the yield thereof will be reduced.

Such a problem may not be so serious if the breakthrough curve for theless readily adsorbable gas component and the readily adsorbable gascomponent in the adsorption column is sufficiently sharp and flat but itbecomes a serious fault when the particle size of the adsorbent islarge, the diameter of the adsorption column is too large as comparedwith the length of the column, a combination of the kind of adsorbentand the kind of the gas component to be adsorbed thereto requires a longperiod of time for attaining the desorption equilibrium, and the periodsof time required for conducting the adsorption, desorption, and purgingopera' tions are shortened.

Furthermore, as mentioned before, the process of this invention ispracticed by repeating the three steps of adsorption, purging, anddesorption or by repeating the four steps of feedback, adsorption,purging, and desorption and thus, in the system of employing a singleadsorption column as illustrated in FIG. I, it is difficult to introducecontinuously the raw gas to be separated into each components into theadsorption column and further the product gas thus separated only indiscontinuous manner, Accordingly, the process of this-inventionillustrated in FIG. 1 may be unsuitable as an aparatus or system forconducting the process in an industrial scale.

Thus, for practicing the process of this invention as illustrated aboveas an embodiment of the fundamental unit process thereof in anindustrial and continuous process, the embodiments as illustrated inFIG. 2 and FIG. 3 of the accompanying drawings are suitable. That is,the process of this invention can be more effectively practiced in anindustrial scale without accompanied with the aforesaid troubles. Thus,these embodiments will be explained below in detail by referring to thefig- Ul'LS.

Now, in H6, 2 is shown an industrially applicable embodiment of thisinvention, in which adsorption columns l6, l7. and 18 each containing anadsorbent are employed. The numerals of from 1 to are valves, thenumeral I8 is a feed gas blower, the numeral is a blower for the readilyadsorbable gas component, and the numeral II is a vacuum pump used inthe CltSc of conducting the desorption step under a pressure lower thanatmospheric pressure. The use of the vacuum pump 21 is of courseunnecessary when the adsorption step is conducted under pressure and thedesorption step is conducted at normal pressure. Furthermore, thenumeral is a feed gas inlet, the numeral 24 is an outlet for the readilyadsorbable gas component, the numerul 23 is an outlet for the lessreadily adsorbable gas component or a gas enriched with the less readilyadsorbable gas component, and the numeral 26 is a tank for the lessreadily adsorbable gas component. The states of the valves l-5 in eachstep are shown in Table 3 in which the mark shows the valve being in anopen state and the mark shows the valve being in a closed state.

For example. as clear from Table 3 and FIG. 2, it will be understoodthat the adsorption column 16 is desorbed in the operation cycle numer lor 2, the adsorption column 17 is desorbed in the operation cycle numbet3 or 4, and the adsorption column 18 in the opera tion cycle numer S or6.

Furthermore. it will be understood that in the operation cycle numer lof Table 3, the adsorption column 16 is in a desorption step, the column17 rests, and the column 18 is in an adsorption step of adsorbing thereadily adsorbable gas component by introducing therein a feed gas.

Table Ill: State ofeacli valve M Opcrulron cycle No No No No No No l 2 35 6 mite Table lllz, State of each valveContinued In the operation cyclenumber 2, the adsorption col umn 16 is in the desorption step as in theprevious step (the operation cycle number I) but because the gas in thetank 22 for the readily adsorbable gas component is sent through thevalve 8 to the adsorption column 17 by means of the gas blower 20, thecolumn I7 is purged by the readily adsorbable gas component thus introduced. In this case, the valve 2 is in a closed state and the valve 3 inan open state, and thus the gas containing a certain amount of the lessreadily adsorbable gas component withdrawn from the opposite end of thecolumn 17 is introduced into the adsorption column 18 through valve 15.Accordingly, when the purge of the adsorption column 17 is sufficientlyconducted until the exhaust gas from the column 17 consists of almostthe readily adsorbable gas component, the exhaust gas is effectivelyused for prepurging the adsorption column 18, which contributes hreatlyto save the amount of the purging gas.

Moreover, it has also been discovered that when the same procedure asthe system as illustrated in H0. 2 is conducted in accordance with theoperation cycles as shown in Table 4, the aforesaid merit is completelylost and the amount ofthe high-pure readily adsorhable gas componentobtained by one desorption step is greatly reduced. That is, when thesystem as illustrated in FIG. 2 is operated in the operation cycles asshown in Table 4, the feedback gas of the less readily adsorbablc gas.the readily adsorbable gas for purging. etc, are successively introducedinto each column and the system can be operated without resting thecolumns. Also. in such case, in each cycle of the operation cyclenumbers 2,4. and 6, two adsorption columns are Connected in series andthus the connected column can be subjected to the pre-purging procedureby the exhaust gas from the first column. Thus, at a Table [V State ofeach valve Operation cycle No No No No No No l 2 3 4 5 6 Valve l3 l4 Aglance, it may be considered that there are no troubles in such anoperation. However, in fact, the operation according to the operationcycles shown in Table 4 is accompanied with the great reduction inefficiency as compared with the operation by the operation cycles shownin Table 3. The reason is believed as follows.

That is, in the operation according to the cycles of the Table 3, forexample. the column 18 is pre-purged by the exhaust gas from column 17in the operation cycle number 2 but is in a rest state in the operationcycle number 3 and any gas is not introduced into the column 18 fromoutside in the step. Therefore, the portion of the adsorption column 18adjacent to the side of the valve [5 will be purged further by the purereadily adsorbable gas component in the subsequent opera' tion cycle 4in such state that the portion has be prepurged by the almost purereadily adsorbable component in the precious operation cycle,3. On theother hand, in the operation by the cycles shown in Table 4, theprocedures upto the operation cycle 2 may be same as above but a feedgas is introduced into the adsorption column 18 in the operation cycle 3and then the column [8 is purged again by the pure readily adsorbablegas component in the subsequent operation cycle 4. Accordingly, thedistribution of the readily adsorb able gas component in the adsorptioncolumn 18 becomes complicated and also the consumed amount of thereadily adsorbable gas component for purging is increased, which resultin lowering the efficiency through the whole process.

Now, returning to the operation by the cycles of Table 3, when almost noless readily adsorbable gas component becomes observable in the gas atthe outlet of the adsorption column 17 in the purging cycle, the systemis converted into the cycle shown by the operation cycle number 3 inTable 3. in this cycle, the adsorption column 17 is subjected to thedesorption operation, whereby the adsorbed readily adsorbable gascomponent is desorbed and stored in the tank 22 by means of the pump 21.A part of the gas thus stored is used as the purging gas for the column18 in the subse quent operation cycle (operation cycle number 4) and theremaining gas may be withdrawn as the product. Similarly, in the step ofthe operation cycle numer 4, the adsorption column 18 is purged by thegas from the tank 22 as mentioned just before and simultaneously theadsorption column 16 is pre-purged and further in the step of theoperation cycle number 6, the adsorption column 16 is purged by thestored gas in the tank 22 and the adsorption column 17 is pre-purged.

As stated above, the steps of the operation cycle numbers 1, 2, 3, 4, 5,and 6 are converted successively when the concentration of the readilyadsorbable gas component in the gas at the outlet side of eachadsorption column in the purging step reaches a predetermined value andit will be easily understood that the concentration of the readilyadsorbable component in the gas may be practiced or confirmed by aproper means, such as a densitometer for such a gas component disposedat or near the outlet side of each adsorption column. However, it willalso be understood that after the relation of the variation of theconcentration of the readily adsorba ble gas in the gas at the outletside of the adsorption columns with the passage of time has beenconfirmed by preliminary experiment, a simple operation such asexchanging the cycles every predetermined period of time by means of,tag, a timer if the composition of the feed gas from the conduit 25 aswell as the flow amount thereof are constant, the amount and the purityof the purging gas from the blower are constant, and also the adsorptionpowers of the ad sorption column l6, l7, and 18 are constant.

Also, the process of the first embodiment of the present invention aspreviously indicated may be practiced in the system illustrated in FIG.2 by operating other valves than the valves 1, 2, and 3 in accordancewith the operation shown in Table Ii but by operating the valve 1 sothat the valve is in a closed state in the step of the operation cyclenumber 3 of Table 3 until the inside pressure of the adsorption column16 reaches almost the pressure in the adsorption step and is in an openstate in the last period of the same cycle, operating the valve 2 sothat the valve is in a closed state in the step of the operation cyclenumber 5 until the inside pressure of the adsorption column 17 reachesthe pressure in the adsorption step but in an open state in the lastperiod of the same cycle, and operating the valve 3 so that the valve isin a closed state in the step of the operation cycle number 1 until theinside pressure of the adsorption column l8 reaches the pressure in theadsorption step but in an open state in the last pe riod of the samecycle. ln this embodiment the use of the tank 26 for the less readilyadsorbable gas component is unnecessary.

Moreover, the second embodiment ofthe present invention as previouslyindicated may be practiced in the system shown in FIG. 2 by operatingother valves than the valves 10, ll, and 12 in accordance with the operation shown in Table 3 but operating the valve 10 so that the valve is ina closed state in the step of the operation cycle number 3 until theinside pressure of the adsorp tion column 16 reaches the pressure in theadsorption step and is in an open state in the last period ofthe cycle,operating the valve ll so that the valve is in a closed state in thestep of the Operation cycle number 5 until the pressure of theadsorption column I? reaches the pressure in the adsorption step but inan open state in the last period of the same cycle, and operating thevalve 12 so that the valve is in a closed state until the insidepressure of the adsorption column [8 reaches the pressure in theadsorption step but is in an open state in the last period of the samecycle.

As mentioned above, the typical example of practicing effectively theprocess of this invention using the three adsorption columns weredescribed by referring to the system shown in FIG. 2. The inventor hasfurther investigated various effective processes of practicing theinvention and as the results thereof has found other embodiment as shownin FIG, 3 of the accompanying drawings. By the embodiment shown in H0.3, the less readily adsorbable gas component and the readily adsorbablegas component can be separated simultaneously in high-pure states andwith good yields in each case. Furthermore, in the embodiment the gasblowers l9 and 20 for sending continuously gases into the system may beones having a low capacity. Thus, the process of the embodiment is moreeffective and preferable for practicing the process of this inventionindustrially and economically.

Now in FIG. 3 the numerals from 1 to 20 are valves, the numerals 2!, 22,23, and 24 are adsorption columns each containing an adsorbent, thenumeral 25 is a blower for the feed gas, and the numeral 26 is a blowerfor the readily adsorbable gas component. Also, the numeral 27 is avacuum pump used in case of conducting the desorption procedure under areduced pressure. Of course, the pump 27 is unnecessary when theadsorption is conducted under pressure and the desorption is conductedunder normal pressure. The numeral 28 is a tank for storing the readilyadsorbable gas component and the numeral 29 is a tank for storing theless readily TABLE V: STATE OF EACH VALVE Operation cycle No. l

product gas composed of the high-pure readily adsorbable gas componentand the numeral 30 is an outlet for the product gas composed of thehigh-pure less readily adsorbable gas component. Furthermore, thenumeral 32 is an inlet for the feed gas to be separated into eachcomponents.

Thus, by operating the four-column system as shown in FIG. 3 inaccordance with the manner as shown in Table 5, the feedback procedureby the less readily adsorbable gas component, the adsorption of thereadily adsorbable gas component in the feed gas, the purging procedureby the pure readily adsorbable gas component under the pressure almostsame as that in the adsorption step. and the desorption under a pressurelower than the pressure in the adsorption step are conductedsuccessively and in order to each adsorption column and the moreeffective process of the second embodiment of this invention includingthe feedback operation can be practiced by the aforesaid process. Thatis, by the process as mentioned above, the highpure readily adsorbablegas component can be withdrawn through the conduit 30 with a high yieldand at the same time the high-pure less readily adsorbable gas componentcan also be withdrawn through the conduit 31.

Also, it will be clear by the below-showing Example 5 of this inventionhow the process of this invention illustrated in Example 2 is excellentin practical use. That is, the dimensions of each adsorption columns andthe nature and amount of the adsorbent used in Example 5 were completelysame as those used in the above indicated examples of this invention butthe particle size of the adsorbent in Example 5 was 4-6 mesh, which wasfar smaller than that of the adsorbent in Reference 2 and Examples 4-6.Also, the amount of the feed gas supplied was 3 liters/min. in Example5, which was as high as about thrice the rate of the introduction of airin Examples 3 and 4. Furthermore, the final vacuum pressure was 73 mm.Hg in Example 5, while it was 50 mm. Hg in Reference 2 and Examples 3and 4 Thus, although the various conditions in Example 5 were fardisadvantageous for conducting the separation of oxygen and nitrogenfrom air as compared with the conditions in Reference 2 and Examples 3and 4, the amount and the purity of nitrogen gas obtained in Example 7was almost same as those in Reference 2 and Examples 3 and 4. This isbecause, as will be described below, in Example 5 the desorption cyclewas repeated every 1.5 minutes and a high-pure nitrogen gas of99.98-99.96 percent in purity was formed in a rate of 480 liters/hour.Therefore, the volume of the nitrogen 5 gas thus obtained was 12 litersper cycle of the adsorption column, which was almost same as the case ofconducting the adsorption process using the single adsorption column inaccordance with the process of this in- EXAMPLE 5 Four adsorptioncolumns each having the same dimensions as in Reference 2 and containingthe same adsorbent as in Reference 2 were arranged as shown in FIG. 3.[n this case, however, the particle size of the adsorbent was 4-6 mesh(Tyler mesh). The minimum pressure in the adsorption column at thedesorption step was 73 mm. Hg and further each operation of thefeedback, adsorption, and purging steps was conducted under almostatmospheric pressure. Also, the period of time required for finishingthe desorption step was 1.5 minutes per adsorption column. The valveswere operated as shown in Table 5.

Under the conditions as mentioned above, air from which carbon dioxideand moisture had been preliminary removed was introduced into theseparation system continuously at a rate of 630 liters per hour and anitrogen gas having a purity of 99.98 99.96 percent was obtained in arate of 480 liters per hour. Also, an oxygen containing gas was obtainedas the less readily adsorbable gas component at a rate of 150 liters perhour and it contained only about 9 percent nitrogen.

What is claimed is:

I. In a process for separating a readily adsorbable gas component from agas mixture of the readily adsorbable gas component and a less readilyadsorbable gas component, which comprises introducing the gas mixtureinto an adsorption column having an inlet and an outlet, and containingan adsorbent to adsorb the readily adsorbable gas component andrecovering the readily adsorbable gas component by desorbing thecomponent thus adsorbed under a reduced pressure, the improvementwherein (1) the adsorption of the readily adsorbable gas component iscontinued until the composition of the gas at the outlet of the columnis substantially the same as the composition of the gas at the inlet ofthe column, and (2) prior to the desorption step, the inside of thecolumn is purged with a substantially pure gas having substantially thesame composition as the readily adsorbable gas component undersubstantially the same pressure as employed in the adsorption step.

2. The process as claimed in claim 1 wherein said adsorbent is preparedby dehydrating a tuff mainly consisting of SiO,,, A1 0 and H 0,containing 1-10 percent by weight of alkali metal and alkaline earthmetal oxides, and having the X-ray diffraction pattern shown in thepreceeding Table I or Table II.

3. The process as claimed in claim l wherein said readily adsorbable gascomponent is nitrogen and said less readily adsorbable gas component isoxygen.

4. A process for separating a readily adsorbable gas component and aless readily adsorbable gas component from a gas mixture thereof, whichcomprises introducing the gas mixture into an adsorption column havingan inlet and an outlet, and containing an adsorbent to adsorb thereadily adsorbable gas component. while recovering the less readilyadsorbable gas component, and then recovering the readily adsorbable gascomponent by desorbing the component thus adsorbed under reducedpressure, the improvement wherein (l) a substantially pure gas havingsubstantially the same composition as the less readily adsorbablecomponent is introduced into the column prior to the introduction of thegas mixture into the column until the inside pressure of the columnbecomes substantially the same as the pressure employed in theadsorption step, (2) the adsorption of the readily adsorbable gascomponent is continued until the composition of the gas at the outlet ofthe column is substantially the same as the composition of the gas atthe inlet of the column, and (3) prior to the desorption step, theinside of the column is purged with a substantially pure gas havingsubstantially the same composition as the readily adsorbable gascomponent under substantially the same pressure as employed in theadsorption step.

5. The process as claimed in claim 4 wherein said adless readilyadsorbable gas component is oxygen.

* t ll

2. The process as claimed in claim 1 wherein said adsorbent is prepared by dehydrating a tuff mainly consisting of SiO2, Al2O3 and H2O, containing 1-10 percent by weight of alkali metal and alkaline earth metal oxides, and having the X-ray diffraction pattern shown in the preceeding Table I or Table II.
 3. The process as claimed in claim 1 wherein said readily adsorbable gas component is nitrogen and said less readily adsorbable gas component is oxygen.
 4. A process for separating a readily adsorbable gas component and a less readily adsorbable gas component from a gas mixture thereof, which comprises introducing the gas mixture into an adsorption column having an inlet and an outlet, and containing an adsorbent to adsorb the readily adsorbable gas component, while recovering the less readily adsorbable gas component, and then recovering the readily adsorbable gas component by desorbing the component thus adsorbed under reduced pressure, the improvement wherein (1) a substantially pure gas having substantially the same composition as the less readily adsorbable component is introduced into the column prior to the introduction of the gas mixture into the column until the inside pressure of the column becomes substantially the same as the pressure employed in the adsorption step, (2) the adsorption of the readily adsorbable gas component is continued until the composition of the gas at the outlet of the column is substantially the same as the composition of the gas at the inlet of the column, and (3) prior to the desorption step, the inside of the column is purged with a substantially pure gas having substantially the same composition as the readily adsorbable gas component under substantially the same pressure as employed in the adsorption step.
 5. The process as claimed in claim 4 whereIn said adsorbent is preapred by dehydrating a tuff mainly consisting of SiO2, Al2O3 and H2O, containing 1-10 percent by weight of alkali metal or alkaline earth metal oxides, and having the X-ray diffraction pattern shown in the preceeding Table I or Table II.
 6. The process as claimed in claim 4 wherein said readily adsorbable gas component is nitrogen and said less readily adsorbable gas component is oxygen. 